Why You Can't Blindly Trust A1C

There is genetics and hemoglobin variants and then among one of the principal reasons. Is the life spans of red blood cells the lifetime of red blood cells is is as low as 81 days in diabetics with poor control, and as high as 146 days in people with normal blood sugars.

So some diabetics may have falsely lower a1c, while people with normal blood sugar may show higher a1cs than others non-diabetics.

http://care.diabetesjournals.org/content/27/4/931.full

Abstract

OBJECTIVE—Subjects with decreased erythrocyte survival have an unusually low GHb percentage. The goal of this study was to determine whether hyperglycemia, as reflected by GHb percentage, is associated with decreased erythrocyte survival.

RESEARCH DESIGN AND METHODS—Erythrocyte survival was quantitated in 23 subjects with type 2 diabetes, and these values were correlated with the subjects’ GHb percentage. Erythrocyte survival was determined from the difference between the subjects’ alveolar carbon monoxide (CO) concentration and atmospheric CO concentration. Reticulocyte counts were obtained in 16 subjects.

RESULTS—Although the vast majority of the subjects had erythrocyte life spans that fell within the normal range (123 ± 23 days), there was a highly significant inverse correlation (r = −0.66, P < 0.01) between life span and GHb percentage, with an average decline in life span of 6.9 days for each 1% rise in GHb. The reticulocyte count inversely correlated with erythrocyte life span (r = −0.77, P < 0.01).

CONCLUSIONS—Hyperglycemia, as evidenced by high GHb percentage, is associated with an appreciable decrease in erythrocyte life span. Because GHb appears to be formed over the lifetime of the erythrocyte, this decreased erythrocyte survival suggests that high GHb percentages may systematically underestimate the true degree of hyperglycemia.

Measurements of GHb and its predominant component, HbA1c, have become the routine means of assessing blood glucose control in patients with diabetes. It is well accepted that glucose combines with Hb via a slow irreversible nonenzymatic reaction, the rate of which is determined by the serum glucose concentration (1,2). Thus, GHb percentage can be used as a time-averaged index of the blood glucose concentration to which the Hb has been exposed. However, unusually low GHb percentages are observed in subjects with hemolytic anemia (3–7). Thus, GHb concentration also is a function of the duration of exposure of Hb to blood glucose, i.e., the life span of the erythrocyte. Of particular interest was a study by Peterson et al. (, which showed that the life span of 51Cr-labeled erythrocytes increased in each of seven subjects when their poorly controlled diabetes was brought under control. This observation suggests that hyperglycemia reduces erythrocyte survival, a phenomenon that would cause high GHb levels to consistently underestimate the severity of hyperglycemia. The small sample size (seven subjects) in the study by Peterson et al. ( presumably is attributable to the time-consuming and cumbersome nature of 51Cr labeling studies, which require repeated blood samplings over a multiweek period to obtain a single erythrocyte survival measurement. We recently described a simple and rapid technique to quantitate erythrocyte survival based on measurements of the concentration of carbon monoxide (CO) in expired air (9,10). In the present study, this technique was used to study the relationship between GHb percentage and erythrocyte survival.

Interesting post Yoly, thanks .I also think another small flaw in HbA1C measurement is the fact that it doesn't give any indication of regular highs or lows. Lots of readings of 9's and 3's for instance ( bit extreme ) could give an HbA1C of around 6 which most would be overjoyed with .

At best it's only a tool for spotting trends but I'm sure my A1c's are falsely lower as I tend to run low haemoglobin levels due to microscopic bleeding in my GI tract due to Crohns disease which means my red blood cells don't live for 90 days...I've asked for a Fructosamine test which is more accurate in my circumstances but I was refused...

Paul1976 wrote:At best it's only a tool for spotting trends but I'm sure my A1c's are falsely lower as I tend to run low haemoglobin levels due to microscopic bleeding in my GI tract due to Crohns disease which means my red blood cells don't live for 90 days...I've asked for a Fructosamine test which is more accurate in my circumstances but I was refused...

Try a vet? Seriously, they use fructosamine all the time.

I ever so slightly expect the reason NICE determined that diabetes must only be diagnosed by A1c was for this very reason, it reduces the number of patients diagnosed.

Nice to see the name of Frank Q Nuttall on the paper, he and Mary Gannon did some sterling work with what they called LoBAG (Low Biologically Active Glucose) diets, low carb by any other name.

Some of these papers were sponsored by the ADA. When they came up with the "wrong" results, they remained on the ADA website but the links were removed so you could only find them if you knew where to look. Haven't been to see if that changed in the meantime.

mo1905 wrote:Interesting post Yoly, thanks .I also think another small flaw in HbA1C measurement is the fact that it doesn't give any indication of regular highs or lows. Lots of readings of 9's and 3's for instance ( bit extreme ) could give an HbA1C of around 6 which most would be overjoyed with .

Yes that is one of the drawback of relying only on A1C to track your diabetes. Many still have periods of very low glucose specially if using diabetes drugs or using insulin getting lower A1C but still suffering hyperglycemia damage after eating.

The bottom line no BG measuring system is that accurate, meters can be plus or minus 20%, although I reckon some are better than that. The same goes for HbA1c tests, you can split a blood sample and send it to two different labs and get significant differences. It's the best we are going to get for a long while and good enough I reckon. Lets face it if we are holding good numbers we are probably doing all we can. All that being said diabetes is a unique chronic disease in so much as we can monitor it ourselves with a simple blood test on a daily basis and not sit around worrying for months for the next hospital test to tell us where we stand.

So many grim disease we could have gone down with, and no chance of controlling or reversing the main symptoms. As chronic diseases go, we are the lucky ones. I have always looked at type two diabetes as a life sentence not a death sentence, and there are plenty of type ones still going strong 60 or 70 years after diagnosis.